Hammer drills are known which are configured to operate according to a drive mode selected by a user from drive modes including a hammer mode (also referred to as a chisel mode) and a drill mode. Some of the hammer drills are configured to lock an operation member for a switch for driving a tool accessory in an ON position in order to keep the switch in an on-state in the hammer mode, and not to lock the operation member in the ON position in the drill mode. For example, in a hammer drill disclosed in Japanese Patent No. 4729159, when a lock member which is movable between a first operating position and a second operating position is moved to the first operating position in the hammer mode, a return path of an operation member to an OFF position is blocked. Thus, the operation member is locked in the ON position.